1. Field of the Invention
The present invention relates to an image forming apparatus capable of restricting copying of a document.
2. Description of the Related Art
In offices and the like, a document printed by a printer is often copied by a copying machine. This may, however, cause serious security problems. For example, if copies of a confidential document distributed at a meeting or the like are made, it is likely that these copies will fall into the hands of third parties.
FIG. 18 and FIG. 19 illustrate exemplary techniques widely used to prevent such a problem. Referring to FIG. 18, an output document contains a warning message indicating that copying is not permitted. FIG. 19 illustrates a technique in which invisible marks that have been recorded, using a special sheet or ink, on a document to be copied are made visible when a copy of this document is output.
However, even if a copy-protection warning is added to a document as illustrated in FIG. 18, it is possible to ignore the warning and make a copy of the document. Therefore, the technique illustrated in FIG. 18 has only a limited effect on copy protection.
The technique illustrated in FIG. 19 involves the use of special consumable items (such as sheets or ink) and a printing apparatus required for using them. This leads to a problem of increased cost.
FIG. 20 illustrates a technique used in recent years. In this technique, a copy-forgery-inhibited pattern or watermark is added in advance to part or the entire surface of an output document. Then, if the output document with a copy-forgery-inhibited pattern or watermark is copied, it can be visually recognized that the resulting material is a copy of the output document. There is also a proposed apparatus which provides a mechanism for shading the entire surface of such a copy.
Additionally, there is a need for a copy restriction method which permits copying of a document a limited number of times, instead of totally inhibiting copying.
In response to such a need, there has been proposed a technique in which a “first-generation-copying inhibiting mark” for inhibiting copying of a document or a “second-generation-copying inhibiting mark” for inhibiting copying of a copy of a document is added in advance as image information to the document, which is then output. If the first-generation-copying inhibiting mark is detected when the output document is scanned, the scanned image of the document is removed. On the other hand, if the second-generation-copying inhibiting mark is detected when the output document is scanned, the second-generation-copying inhibiting mark is removed and a first-generation-copying inhibiting mark is newly added to the scanned image, which is then output (e.g., see, Japanese Patent Laid-Open No. 2000-184178).
The invention disclosed in Japanese Patent Laid-Open No. 2000-184178 is effective, as illustrated in FIG. 17, in permitting up to predetermined-generation copying and inhibiting further-generation copying.
The invention disclosed in Japanese Patent Laid-Open No. 2000-184178 is effective when applied to an operating environment, such as an office, where only copying machines with the above-described configuration are used. However, in an operating environment where copying machines which do not have the above-described configuration are also used, it is difficult to ensure information security, since such copying machines do not support the copy restriction function described above.
In other words, the invention disclosed in Japanese Patent Laid-Open No. 2000-184178 is effective in preventing information leaking where only copying machines with the copy restriction function are used, but reduces its practical effects by half in an operating environment where copying machines which do not support the copy restriction function are also used.